This invention relates to spring foundation units, and more particularly to a spring foundation unit having one or more pairs of inner border members on the top and bottom surfaces of the unit for increasing the firmness of the foundation unit.
Spring foundation units are well known, as exemplified by U.S. Pat. Nos. 1,237,727 and 2,184,517. Additionally, spring foundation units having one or more inner border members for increasing the firmness of the unit are common, as exemplified by U.S. Pat. Nos. 2,383,157 and 3,242,505.
In the above-identified U.S. Pat. No. 3,242,505, a spring unit is disclosed which has top and bottom inner border members which are separated by at least one width of the coil springs of the unit from the outer border wire of the unit at all times. A plurality of secondary connecting elements extend between opposite end portions of the inner border member. The inner border member and secondary connecting elements are alleged to increase the firmness of the foundation unit.
A substantial disadvantage of prior art apparatus such as U.S. Pat. No. 3,242,505 is that only a certain degree of increased firmness can be attained by utilizing the inner border member and secondary connecting elements because the combined inner border member and connecting elements act as an island of support. In addition, although increased firmness is attained, the stiffer the inner border member and secondary connecting elements become, the less able the foundation unit is to conform to the contours of a user's body. Thus, although the foundation unit is firm, it is also unforgiving and not suitable for providing rigid, yet comfortable support demanded by most consumers.